STEM Readiness: Physics Readiness - Kinematics: Circular Motion - Angular Velocity, Centripetal Acceleration, Period and Frequency

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes include Bacteria and Archaea; eukaryotes include animals, plants, fungi, and protists.
• Prokaryotic DNA is located in the nucleoid, a region without a membrane; eukaryotic DNA is enclosed within a membrane-bound nucleus.
• Prokaryotes have 70S ribosomes (30S + 50S subunits); eukaryotes have 80S ribosomes (40S + 60S subunits).
• Mitochondria and chloroplasts contain 70S ribosomes, supporting their origin via endosymbiotic theory.
• Prokaryotic cell walls are made of peptidoglycan (in bacteria); archaea lack peptidoglycan but may have pseudopeptidoglycan.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack cell walls.
• Mycoplasma, a bacterium, lacks a cell wall and is resistant to antibiotics like penicillin that target peptidoglycan.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane with embedded proteins.
• Eukaryotes have internal membrane systems including the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and mitochondria; prokaryotes lack these organelles.
• The nuclear envelope in eukaryotes is a double membrane with nuclear pores that regulate transport.
• Nucleolus is present inside the eukaryotic nucleus and is the site of ribosomal RNA (rRNA) synthesis.
• Prokaryotes reproduce by binary fission; eukaryotes divide by mitosis and meiosis.
• Eukaryotic mitochondria have their own circular DNA, similar to bacterial chromosomes.
• Chloroplasts are found in plants and some protists; they perform photosynthesis and have thylakoid membranes.
• Lysosomes (in animal cells) contain hydrolytic enzymes for intracellular digestion; absent in most plant cells.
• Peroxisomes contain oxidative enzymes like catalase and are involved in lipid metabolism and detoxification.
• Smooth ER synthesizes lipids and steroids and detoxifies drugs; rough ER has ribosomes and synthesizes proteins for secretion.
• Golgi apparatus modifies, sorts, and packages proteins into vesicles for transport to lysosomes, plasma membrane, or secretion.
• Cytoskeleton (microtubules, microfilaments, intermediate filaments) is present in eukaryotes; prokaryotes have homologs like FtsZ but lack true cytoskeleton.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and move in a whip-like fashion.
• Red blood cells (erythrocytes) in mammals lack a nucleus and mitochondria to maximize hemoglobin content.
• Plant cells have a large central vacuole that maintains turgor pressure; animal cells have small or temporary vacuoles.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having double membranes, 70S ribosomes, and independent division.
• Archaea lack peptidoglycan and have ether-linked lipids in their membranes, unlike bacteria and eukaryotes.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelles, including exceptions.

Common Traps (3–5 factual traps)

• Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.
• Trap: Ribosome size directly correlates with cell complexity – Fact: Mitochondria and chloroplasts in eukaryotes have 70S ribosomes, not 80S.
• Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes.
• Trap: Prokaryotes have no internal membranes – Fact: Some prokaryotes have intracellular membranes (e.g., photosynthetic membranes in cyanobacteria).
• Trap: Eukaryotes are always larger because they have more DNA – Fact: Genome size does not correlate with cell size or organism complexity (e.g., some protists have larger genomes than humans).

Practice MCQs (5–7 questions)

Question: Which of the following is a structural feature found in eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) 70S ribosomes
C) Circular DNA
D) Membrane-bound nucleus
Answer: D
Explanation: Only eukaryotes have a membrane-bound nucleus.
Why the top distractor is wrong: Circular DNA is present in both prokaryotes and eukaryotic mitochondria/chloroplasts.

Question: A cell is observed to have a cell wall, chloroplasts, and a large central vacuole. Which type of cell is it most likely to be?
A) Fungal cell
B) Animal cell
C) Bacterial cell
D) Plant cell
Answer: D
Explanation: Plant cells uniquely have chloroplasts, a large central vacuole, and a cellulose cell wall.
Why the top distractor is wrong: Fungal cells have cell walls (chitin) and vacuoles but lack chloroplasts.

Question: Which of the following provides the strongest evidence for the endosymbiotic theory?
A) Mitochondria are found in all eukaryotic cells
B) Mitochondria have their own 70S ribosomes and circular DNA
C) Mitochondria are surrounded by a single membrane
D) Mitochondria replicate independently of the cell cycle
Answer: B
Explanation: Mitochondria having 70S ribosomes and circular DNA closely resembles bacteria, supporting bacterial origin.
Why the top distractor is wrong: Mitochondria are surrounded by a double membrane, not single.

Question: Which organism lacks a cell wall and is therefore naturally resistant to penicillin?
A) Escherichia coli
B) Bacillus subtilis
C) Mycoplasma pneumoniae
D) Saccharomyces cerevisiae
Answer: C
Explanation: Mycoplasma lacks a cell wall and thus is unaffected by penicillin, which inhibits peptidoglycan synthesis.
Why the top distractor is wrong: E. coli has a peptidoglycan cell wall and is typically susceptible to penicillin.

Question: Where are ribosomal subunits assembled in a eukaryotic cell?
A) Rough ER
B) Nucleus
C) Nucleolus
D) Golgi apparatus
Answer: C
Explanation: The nucleolus is the site of rRNA transcription and ribosomal subunit assembly.
Why the top distractor is wrong: The nucleus contains the nucleolus, but subunit assembly occurs specifically in the nucleolus.

Question: Which of the following is true of both prokaryotic and eukaryotic plasma membranes?
A) Composed of phospholipid bilayer with embedded proteins
B) Contain peptidoglycan
C) Surround the nucleus
D) Contain 80S ribosomes
Answer: A
Explanation: Both cell types have a phospholipid bilayer plasma membrane with proteins.
Why the top distractor is wrong: Peptidoglycan is only in bacterial cell walls, not membranes.

Question: Which organelle is responsible for modifying and packaging proteins for secretion?
A) Rough ER
B) Smooth ER
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins into vesicles for secretion.
Why the top distractor is wrong: The rough ER synthesizes proteins but does not package them for secretion.

Last?Minute Revision (20–25 one?liners)

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes lack a nucleus; DNA is in the nucleoid.
• Eukaryotes have 80S ribosomes; prokaryotes have 70S.
• Mitochondria and chloroplasts have 70S ribosomes – supports endosymbiosis.
• Bacterial cell wall = peptidoglycan; plant = cellulose; fungi = chitin.
• Mycoplasma has no cell wall – naturally penicillin-resistant.
• Red blood cells lack a nucleus and mitochondria.
• Both domains have phospholipid bilayer plasma membranes.
• Eukaryotes have internal membranes (ER, Golgi, nucleus); prokaryotes do not.
• Nuclear pores regulate molecule transport in and out of nucleus.
• Nucleolus = site of rRNA synthesis and ribosome assembly.
• Binary fission = prokaryotic division; mitosis = eukaryotic nuclear division.
• Mitochondrial DNA is circular, like bacterial DNA.
• Chloroplasts have thylakoids and perform photosynthesis.
• Lysosomes are in animal cells; contain hydrolytic enzymes.
• Peroxisomes break down fatty acids and detoxify hydrogen peroxide.
• Smooth ER = lipid synthesis; rough ER = protein synthesis.
• Golgi apparatus = modifies and sorts proteins into vesicles.
• Cytoskeleton (microtubules, actin) is eukaryotic-specific.
• Prokaryotic flagellum = flagellin, rotates; eukaryotic = 9+2 microtubules, whips.
• Double membranes exist in nucleus, mitochondria, chloroplasts.
• Endosymbiotic theory supported by organelle DNA, ribosomes, and fission.
• Archaea lack peptidoglycan and have ether-linked membrane lipids.
• Some prokaryotes (e.g., cyanobacteria) have internal membranes for photosynthesis.
• Verify from standard textbook: Exact lipid composition in archaeal membranes.